This invention relates to a tire pressure indicator, and particularly to a kind of tire pressure indicator having a pressure sensor and a separate inflating pin arranged therein for monitoring and warning the user of a deficiency of pressure in an associated tire, as well as for preventing the air pressure in an associated tire from leaking out in case a malfunction of said indicator occurs thereat.
Conventionally, tire pressure is usually checked either by using a pressure gauge or by feeling the tire. The former method is normally done by specialists while the latter method is usually adopted by ordinary people, who press the tire with their hand or knock on the tire with a hammer or their foot. In order to provide an automatic tire pressure detecting arrangement, a tire pressure detector has been developed to meet the demand of ordinary people for accurate and reliable tire pressure measurement. Such a tire pressure detector is described in U.S. Pat. No. 4,726,223, issued to this applicant.
The main feature of the tire pressure detector, (presented with two embodiments), disclosed in said Patent Specification, resides in a hollow cylindrical case having an open end thereof screw-connected to the inflating valve of an associated tire with a pin which is inserted into the inflating valve so as to enable the pressure of said tire to pass through an air channel provided in said hollow cylindrical case and push upward a piston member movably located and remaining therein so that an axial rod, (in a first embodiment), extends out of the hollow cylindrical case or a light bulb, (in a second embodiment), which remains unlit thereat, indicating that the tire pressure is sufficient. If the tire pressure is insufficient, the piston member in the hollow cylindrical case will drop and the top of said axial rod (in the first embodiment) will be lowered down, or said light bulb (in the second embodiment) will be lit thereat, as a result of the contact made between said light bulb and the terminal of a battery disposed therein, serving as a warning indicator thereat. Although said tire pressure detector (in two embodiments) can function well under normal conditions, it suffers from a drawback as follows:
Since the piston member of said air pressure detector is positioned within said hollow cylindrical case and supported by a cap member screw-connected to the upper portion of said hollow cylindrical case, if said cap member is intentionally loosened or accidentally damaged, said piston member will become unattached therein while the open end of said hollow cylindrical case, together with the pin, remains secured on the inflating valve of said tire so that the air pressure in the tire will leak out through the air channel of said hollow cylindrical case, causing a considerable deficiency thereof.